My Sister-in-law had Parkinson's disease. It was advancing to the point that she was unable to function and medication was having little effect. She agreed to an experimental brain implant that was to reduce or possibly eliminate the shaking. Well, things did not go at all as expected. Not long after being implanted she started to exhibit irrational and violent behavior. It would come in episodes, where she would be normal for a while and then erratic. As time went by the erratic behavior became longer lived and more violent, to the point that she all but destroyed her carousel horse collection, which was her pride and joy, as well as being down right mean to everyone around her. From what little I observed, it was very similar to the effects of Alzheimer's disease, of which I have some experience through a family member. Not too long before her death, during one of her lucid moments, she broke down into tears and told her husband that during her erratic times she was inside watching herself doing these things, yet was unable to stop herself. It was as if something else were driving her body and she just stood by helpless to stop it. She felt guilt and remorse at her actions and was basically asking for forgiveness. She died not too long after.

For me, just imagining this type of situation is enough for me to not want anything implanted in my brain. If I ever happen to be in a situation similar to her's I might think differently, or I might be a bit more accepting of my situation considering the possible alternative.